Exhaust gas recirculation (EGR) for internal combustion engines is known. Some engines may also cool the recirculated exhaust gas in EGR coolers. In an engine having a turbocharger, a difference in pressure between the exhaust system and intake system of the engine may determine the maximum amount of exhaust gas that may be recirculated from the exhaust into the intake of the engine.
The pressure of exhaust gas in the exhaust system during operation of the engine is referred to as exhaust back pressure (EBP). Similarly, the pressure of air or a mixture of air and exhaust gas in the intake manifold of the engine is referred to as intake manifold pressure or manifold absolute pressure (MAP) during operation of the engine. An EGR valve is usually employed to fluidly connect the exhaust and intake manifolds. When the EGR valve is opened, exhaust gas flows from the exhaust system into the intake system of the engine. Primary factors that determine the capacity of the EGR system on an engine to flow exhaust gas are the size of the EGR valve opening, and a difference of pressure between EBP and MAP, typically referred to as Delta P.
For emissions control reasons, some engines may require more EGR gas for mixing with the intake air than the engine is able to provide during operation, partly because many engines are advantageously designed to run under low Delta P conditions that are conducive to high fuel economy. Nevertheless, even under conditions of low Delta P, the demand for EGR gas flow increases as emissions requirements for the engine become more stringent.
There have been many methods to augment EGR gas flow on an engine having low Delta P during operation. One method uses an intake throttle valve, configured to constrict air flow into the intake manifold of an engine that is placed at a location upstream of the point of mixing of exhaust gas and air in the intake system. By closing the intake throttle valve, the MAP is lowered and Delta P increases. One disadvantage of this method is that pumping losses in the engine increase, thus lowering fuel economy and the power output of the engine.
Accordingly, there is a need for augmentation of EGR gas flow in an engine having a turbocharger that does not depend on the use of an intake throttle valve or other methods.